Introduction: Measurement and emergency preparedness -- Defining and demonstrating response reliability analysis -- Describing a chlorine release scenario and relevant response parameters -- A simplified model of an emergency response to a chlorine release -- Exploring what can go wrong during a chlorine response operation: identifying relevant failure modes -- Assessing the probability, effects, and severity of failure modes: an exploratory analysis using response after-action reports -- Concluding observations -- Appendix A: Approximating response reliability curves -- Appendix B: Correspondence between the chlorine response model used in this analysis and other ways of categorizing or organizing response operations -- Appendix C: Description of components of the RAND Chlorine Response Model not covered in the text -- Appendix D: Failure trees for all elements of the response model -- Appendix E: Counts of failure modes identified per analyzed after-action report -- Appendix F: List of after-action reports reviewed and analyzed.